This application relates to and incorporates herein by reference Japanese Patent Applications No. 11-55680 filed on Mar. 3, 1999 and No. 11-300467 filed on Oct. 22, 1999.
The present invention generally pertains to imaging apparatuses such as an optical microscope, an electron microscope, an optical telescope and an electronic camera. More particularly, the present invention pertains to a total focus imaging apparatus using a variable-focus lens.
As conventional technologies, the following focusing technologies are disclosed in JP-A-9-230252 (U.S. Pat. No. 5,917,657).
In one imaging technology, while the focal position relative to an object of observation is being moved back and forth at high speeds, that is, the distance from a lens to a focus plane is increased and decreased at high speeds, an image is displayed in real-time manner. This technology thus utilizes the fact that only a portion with a clear focused contour is visually recognized as a retina residual image. By utilizing a physiological residual-image phenomenon, this technology is capable of letting the observer visually recognize an image with the entire object of observation brought to a focus. Thus, this imaging technology is suitable for, among others, a case in which the object of observation is moving.
However, this technology also allows a blurring image not brought to a focus to be created on the retina as an image. In this case, an out-of-focus time is generally longer than an in-focus moment. Thus, this technology has a problem of providing the observer with a feeling to receive a slightly blurring image from the sense of sight. That is, with this technology, it is impossible to obtain an image with all portions of an observation object brought completely to a focus. The technology raises a problem of a slightly blurred feeling in the sense of sight and a problem of causing the eyes to get tired easily. There is also raised a problem that an image completely brought to focus can be merely recognized visually but such an image cannot be photographed and printed.
The second imaging technology is an application of the above imaging technology whereby two imaging apparatuses are directed to an object of observation at a parallax to display photographed images on the right and left eyes so as to allow the observer to see the object of observation with the two eyes. This second technology provides an effect of an ability to visually recognize an image giving a stereo sense to the observer in real-time manner.
However, the second technology has the same problems as the first imaging technology in that the second technology is not capable of presenting an image completely brought to a focus. In addition, since both the first and second imaging technologies are not capable of generating a stereo numerical model of an observation object, it is impossible to present an end-face diagram showing a cross-sectional shape and to display an image obtained as a result of a continuous synthesis of crane-shot images.
It is thus an object of the present invention to generate an image with all portions of an observation object brought to a focus in a semi-real-time manner and to allow an image to be displayed in a variety of display formats by generating a stereo numerical model showing a stereo shape of an observation object.
According to the present invention, a total-focus imaging apparatus is constructed with a variable-focus lens, an actuator for the lens, an image-pickup device, an image memory for storing image signals produced from the image-pickup device, and an image processing circuit for determining an image signal most brought to a focus thereby to determine either an image with all portions of an observation object or a stereo numerical model showing a stereo shape of the observation object.
Preferably, the determination is made based on a polarity inversion of differences in pixel luminance of each pixel between focal positions, a maximum of absolute values of differences in pixel luminance of each pixel between focal positions as a criterion, a minimum of entropy values of image segments of the images at the focal positions, or the like.
In the case of determining the stereo numerical model, a noise elimination filter is used for eliminating high space frequency noise. The filter may be a digital filter for carrying out normal transformation for once transforming the stereo numerical model into space frequency components, for filtering for eliminating high frequency components from the space frequency components, and for executing an inverse transformation for restoring the space frequency components with the high frequency components removed back to the stereo numerical model. Alternatively, the filter may be a digital filter for handling the image signals for each image segment comprising a plurality of pixels, and taking either a luminance value observed most frequently in an image segment or an average of luminance values in an image segment as a uniform value of the image signals of pixels in the image segment.